The transaction is still subject to regulatory approval and stockholder approval. SoftBank and Overland Park, Kan.-based Sprint expect the deal will close in mid-2013. This is the largest-ever overseas acquisition by a Japanese company.

Last year, AT&T proposed to buy T-Mobile for $39 billion, but the deal was stopped by regulators who argued it would reduce competition, limit consumers’ choices in wireless providers and raise prices for mobile services.